CA1052933A

CA1052933A - Polypropylene molding composition and process for its preparation

Info

Publication number: CA1052933A
Application number: CA224,154A
Authority: CA
Inventors: Helmut Strametz; Hans J. Leugering; Manfred Engelmann; Kurt Rust
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1974-04-08
Filing date: 1975-04-07
Publication date: 1979-04-17
Also published as: FR2266721B1; AU7988975A; IT1034936B; US3998911A; IN140973B; NL7503966A; DK147475A; AR208402A1; FR2266721A1; ZA752172B; LU72222A1; DE2417093A1; BE827680A; JPS50142652A; DE2417093B2; ES436227A1; GB1508033A

Abstract

POLYPROPYLENE MOLDING COMPOSITION AND PROCESS
FOR ITS PREPARATION
Abstract of the disclosure A polypropylene molding composition having an excellent impact strength at a temperature down to -60°C and simultane-ously a good hardness contains of from 70 to 90% by weight of a polypropylene, 2 to 10% by weight of an ethylene propylene copolymer and of from 8 to 25% by weight of a polyethylene and is distinguished by a melt index MFI 230/5 lower than that of the polypropylene contained therein and simultaneously super-ior by the coefficient 1.3 to 7.0 to that of a polypropylene prepared in the presence of the same catalyst as the molding composition and having the same RSV(reduced specific viscosity)

Description

~ HOE ?4~F 101 ~' lOS'~933 It i~ known that ethylene, propylene and higher ¢-ole-fins as well as their mixtures ~ay be polymerized in the presence of complex metal-organic mixed catalysts. For this purpose generally are used combination~ of compoundSof ele-ment~ of the first to the third main group with those of the4th to the 6th subgroup of the Periodic Table. The mole-cular weight of po~ymerY prepared in suspension, soLution or in a gaseous phase in the presence of these catalysts may be.in~luenced by the addi.tion of suitable regulators as well as by the reaction temperature to an extent of from S O -.
to 5,000,000. There are known highly stereospecific catalyst systems enabling tranforming propylene to more than 95~ into isotactic, i.e. crystallisable polymer, by a suitable mode ~ -of carrying out the reaction. The .avantageous mechanica-i properties such as a high hardness, stiffness` and dimens1o~ ~
nal stability of articles madeof such a material may be - :
attributed to the high cry~tallinity. On the other hand the relatively high second order transition temperature Tg of the isotactic polypropylene at low temperatures causes a con-siderable decrease of impact strength, tensile strength and flexural strength, which may already be oberved at a tempera-ture of less than ~10C. This inconvenient of the crystalline polypropylene demanded improving the impact strength at low temperatures by admixing component~ thereto loosing their elastic properties only then cooling them to an essentially lower temperature. Ethylene propylene rubber (EPR) as well as polyethylene or combinations of both components are used above all for such a modification by the addition of elasto-29 mers.
'.

~ - 2 -~ HOE l4/F 101 (` ~052933 ~,.J
Such impact resistant mixtures of a low brittle point con~isting of an essentially cryRtalline ethylene propylene copolymer containing a propylene homopolymer bloc and of an essentially linear polyethylene have already been described (cf. German Au~legeschrift No. 1,569,351).
The impact strenth o~ polypropylene at low temperatures may moreover be improved by preparlng in situ mixtures with portions of elastomers of a low Qecond order transition tempe-rature. Thi8 may be realised by adding in a controlla~b manner a suitable comonomer prior to, after homopolymerization or in the course of the homopolymerization of the propylene, where-by a copolymer and/or a second homopolymer is obtained. It is known, for example that propylene may be firstly polymer--ized alone until an essential part is transformed into poly-propylene. Thereafter ethylene is introduced into the reaction mixture without removing the unpolymerized propylene, so that an ethylene propylene copolymer and polyethylene are formed (cf. Britlsh Patent Specification No. 970,479, US Patent Specification No~. 3,301,921, 3,378,608 and 3,454,675). It i~ true that molded article~ prepared from polymer mixture~
obtalned in the aforesaid manner ha~e an improved impact -~trength at temperatures down to -40C, but only an unoatis-rac tory hardne ~ s .
It has now been found that a polypropylene molding compo-oiton ha~ing an excellent lmpact Qtrength at a temperaturedown to -60C and at the oame tlme a good hardne-~s may be pre-pared by flr~tly con~ertlng propylene into a hlghly cryotalllno polypropylene, lntroducl~g at a certain propylene reoidual 29 partlal prescure ethylene into the reaction mlxture ln order - 3 ~

, C 105'~933 to obtain an ethylene propylene copolymer having anonuniform monomer dispersion and by terminating the polymerization after a con~iderable quantity Or polyethylene has been formed.
The invention consequen~y relates to a polypro~ylene mol-ding composition consisting Or from 70 to 90~ by weight Or a polypropylene,

2 to 10~ by weight Or an ethylene propylene copolymer and o~
from 8 to Z5% by weight Or a polyethylene, wherein the melting index MFI 230/5 is lower than that Or the polypropylene contained therein and ~imultaneously higher by the coefficient 1.3 to ~.0 than that of a polypropylene pre-pared in the presece Or the same catalyst as the molding composition and ha~ing the same reduced specific Yiscosity (RSV). -~
Ob~ect Or the invention further is the process for pre-paring said polypropylene molding composition as well as its method of using for preparing molded articles.
The molding composition according to the invention contains from 70 to 90, preferably from 75 to 85~ by weight of polypropylene, 2 to 10, preferably from 3 to 8% by ~eight Or ethylene propylene copolymer and from 8 to 25, preferably ~rom 12 to 17~ by weight Or polyethylene ?
in a finely dispersed form. The polypropylene is highly cry-~talline and has a melt index MFI 230/5 determined according to ASTM D 1238-62 T Or from 5 to 80, preferably of from 10 to ~0 g/10 minutes. The ethylene propylene copolymer has a !9 reduced ~pecific viscoslty (RSV= ~ 9pOC-/C) Or at least 2.0 dl/g ' ' ' ' '' ~ . ' ' ' ' ~ 101 ~ 105Z933 and a monomer di~persion not chemically complete uniform.
The polyethylene contained in the molding composition according to the invention maximally contains 0.5~ by weight of sh~rt chain ramificationY in tha form of incorporated propylene molecules. The melt index MFI 230/5 of the polypropylene molding composition is inferior to that of its polypropylene portion and simultaneously superior by the coeffdcient 1.3 to 7.0, preferably of from 2.0 to 5.0 to that of a polypropylene prepared with the same catalyst system as the molding compo-sition and having the ~ame RSV.
The polypropylene molding composition has the great ad-vantage that it may be directly used for preparing plastics articles owing to its coarse powdered character without pre-vious homogenization in an extruder, ~neader or similar aggregates. Owing to the fact that the melt index of the molding composition may vary within wide limits, it may be practically processed by all known methods for thermoplastics such as extruding, blowing of the extruded material , injection molding etc. The molded articles prepared by said processes compared to molded articles prepared from a polypropylene of the same melting viscosity have a slightly reduced hardness, but an excellent impact strength at all temperatures down to -60C.
In the process according to the invention for preparing the polypropylene molding compositon according to the invention the monomer gases are added in three steps ~o that the poly-propylene portion i9 in the range of from 70 to ~0~ by weight.
The polypropylene portion to be firstly prepared is highly 29 crystalline, which property is obtained by using a considerably - 5 ~

HOE ~/F 101 ~ ~o5'~933 stereospecific catalyst system. ~or thi~ purpose there may be used a combination of TiC13 containing component prepared by reducing TiC14 with aluminium or aluminium diethylchloride or aluminium ethylsesquichloride and submitted to a thermal sccondary treatment using aluminium diethylmonochloride as ; ~ activator. A TiC13 component treated with a complexing com-: . . .
pound may also be used or the stereospecific effect of the catalyst system may be improved by adding so-called third components to the polymerization mixture or both methods may be combined.
A suitable TiC13 component may be prepared, for e~ample~
~y reducing titanium tetrachloride with aluminium diethyl-chloride or ethylsesquichloride at a temperature of from -10 to ~5C in an inert hydrocarbon, whereby a molar ratio of àluminium diethylchloride - being contained in the sesqui-c~loride - to titanium tetrachloride of from 1.6 to 2.0, pre-ferably of from 1.6 to 1.7 is maintained, and by heating sub-sequently the precipitate obtained for a certain period in an inert hydrocarbon and washing it several times with the same liquid after having separated the hydrocarbon in order to remove soluble by-products. The heating and washing pro-:
cess may be optionally repeated once or several times, ~hile increasing the temperatures each time without e~ceeding 140 C.
A TiC13 containing catalyst component (in the example denominated Kl) especially suitable for preparing the molding . , .
composition according to the invention may be prepared as followss 190 g of TiCL4 ln the form of a 48~ ~olution in a benzine 29 fraction having A boiling range Or from about 140 to 170 C are "- ' , - ' "' ' `' `' ' ' ' ~' ~OE 74/~ 101 ' ( `
~ 05,~9 33 introduced into a 6 flask pro~ided with a stirrer, a drip funnel and an inlet tube for nitrogen and cooled to -2 C.
393 ml of aluminium ethylsesquichloride (45.5~ by weight of Al(C2H5)2Cl), dissolved in 2.3 litres of the same benzine fraction are introduced thereto dropwise within 8 hours while stirring. The mixture obtained is allowed to stand to finish the reaction for 2 hours at 0C and for 12 hours at room temperature. Thereafter the precipitate is washed with a fresh dispersing agent until the chorine content of the o~er-lying liquid decreases to less than 0.1~ by weight. The sus-pension is then heated to 95 C while stirring and maintained at this temperature for 4 hours. After reflushing the solid material with fresh dispersing agent the reaction mixture i~
once more subjected to a heat treatment (10 hours at 110Cj, whereupon the dispersing agent is replaced a last time. The content of TiCl3 of the suspension is determined by means of a Ce-IV solution.
The catalyst component K2 used in some of the examples is prepared in the same manner, but by using 190 g of TiCl4 and 221 ml of aluminium ethylsesquichloride.
Another TiCl3 component may also be used, provided that it constitutes a highly stereospecific catalyst system in combination with the aforesaid activator, for example, commercial catalyst components of the composition TiCl3 1/3 Such a TiCl3 containing catalyst component mày also be prepared in the following way:
1400 g of titanium tetrachloride are reacted with 27.0 g of ~;; 29 metalic aluminium powder in the presence of 18.0 g of _ 7 _ .

, HOE 71-/~` 101 C 105'~933 aluminium chloride in a ~tainles,~ steel a~toclave for 20 hours '~ at 200C. The unreacted titanium tetrachloride and the free aluminium chloride are removed from the reaction product by distillation at atmospheric pressure. The remaining solid matter is heated for 5 hour~ at 200C at a reduced pre~sure of 0.2 mm Hg in order to completely re~o~e the titanium tetrachlo-ride. 570 g of a slightly purple colored compound conta$ning titanium trichloride are obtained. ~ ' 30 g of the compound obtained are filled each time in a cyclindric container of stainles~ steel having a capacity of 800 ml and ground for 24 hours in a nitrogen atmosphere in the presence Or 100 ball~ of stainless ste'el having a diameter of 16 mm at a ~elocity of 140 revolutions per minute until the X-ray diffraction pattern of thel - and ~-structure can no longer be identified.
Suitable complexing compounds for ~xample are ethers, thioethers, thiols, phosphines,amines, amides, ~etones, esters, eopecially esters of the formuia R - O - R
wherein R i8 an alkyl radical having from 1 to 15 carbon atoms. Suitable third components for improving the stereo-specifity for example, are cyclopolyenes and pho~phoric acid amides, especially cycloheptatriene and hexamethyl phosphoric acid trisamide.
,` 25 ~he polymerization proceY~ according to the in~ention i~ ' effected in an inert dihent or in the gaseous phase. Ao d~-luents there may be u~ed aliphatlc or cycloaliphatlc hydro-carbons suoh as pentane, hexane, heptane, cyclohexane, 29 methylcyclohexane. Moreover there may be uoed aromatlc hydro-' - 8 .. ~ , . . . .
', ' - ; '' :

, , HOE 74/F 101 ~05'~933 carbons Yuch as benzene, ~ylene or benzine or hydrogenated dleseloil fractions which have been carefully freed from oxy-gen, sulfur compounds and humidity.
The catalyst concentration and the temperature and pressure conditions are cho~en as for a propylene homopoly-merization with the catal~st systëm used.
; The polymerization is realised at a pressure of from 0.5 to 40 kg/cm , preferably Or from 1 to 35 kg/cm , thc reac-tion temperature being in the range of from 40 to 110 C, pre-ferably of from 50 to 90 C, especially Or from 55 to 85C.
The individual polymerization steps may al~o be carried out at different temperatures. The molecular weight and conse-quently the melt visoosity of the polymer may be regulated by the choise of the reaction temperature and by using advantage-ously hydrogen admixed to the monomer to be introduced into the reaction mixture in such a quantity that from O.i to 20~ by ~olume calculated on propylene or from 1 to 50% by volume calculated on ethylene are contained in the gas zone. In the second polymerization step however hydrogen is not generally added to the reaction mixture from the exterior. The quantity ~ Or the TiCl3 containing catalyst component depends on the ; activity and on the reaction conditions, especially On the pres~ure and the ~emperature used. The molar ratio of TiCl3 to aluminium dialkylmonochloride is in the usual range of . ~ .
rrom 1:1 to 1t5 depending on the purity of the monomer and the dispersing agent.
' The ethylene propylene copolymer contained in the moldlng composition does not have a chemically completely uniform 29 monomer dispersion , i.e. it contains a portion of longer . ~ .

~ HOE 74/~ 101 C~' ~o5~933 monomer sequences. This i~ obtained on the one hand by usin~
a he~erogeneous catalyst system a~d on the other hand by the fact that care is taken that the concentraction of both mono-mers does not remain constant during the whole period of their presence in the reaction mixture, i.e. that the mono-mer proportion changes during the copoly~erization period.
.
~ When carrying out the reaction continuously~the aforesaid ; situation i~ obtained by copolymerizing in at least two cas-cade connected reactors wherein varying monomer c~ncentrations are establi~hed)the propylene concentration in the ~econd reactor beingmaintained at a lower level than that in the first reactor.
The most advantageous condition is to assure each cata-lyst particle has the possibility to form a polymer grain of 5 15 the composition according to the invention. This may be ~ -effected especially by polymerizing the second monomer in a ~ reactor system, wherein the resting times are very short, .
for example in a reaction tube having only a little reflux~
wherein the ethylene propylene proportion increases from the be~inning to the end.
The reaction time required for preparing the ethylene propylene copolymer is short owing to its relatively small portion by weight and the propylene quantity used is small~
too. This signifies that ethylene may be introduced at a ~ 25 relatively low propylene partial pressure of less than 0.5, -~ ~referably of 0.3 kg/cm when using a liquid hydrocarbon as reaction medium. Owing to the good solubility of the propy-lene the concentration is nevertheless sufficient for poly-29 merizing.

- 10- ' .

. :. ~ , , . : : :

- ~ - ~ .

~ ~IOE 74/~ 101 f, '105'~!~33 The composition of the ethylene propylene copolymer and its portion in the polypropylene molding compo~ition depends on its intended use. Both factors may be influenced by the propylene residual content at the beginning of the ethylene propylene copolymeri~ation and by the ethylene propylene molar ratio in the course of the copolymerization. It ~ay be in the range of from 90:10 to 25s75, preferably of fr~m ~j:t5 to .
40t60.
When the partial pressure Or the propylene above the reaction mixture has decreased to less than 0.001 kg/cm , the-preparatlon of polyethylene is ~tarted in a third step by in-troducing ethylene, which polyethylene has a small quantity of short chain ramifiactions because of the occasional incor-portions Or propylene molecules still being present.
;~ 15 Working up of the suspension obtained at the end of the polymerization is effected in known manner, for oxample by treating it with a suitable alcohol capable of dissolving catalysts residue~. The suspension may then be washed and dried or the residue~ of dispersing agent are removed by a 8team distillation followed by drying. Working up of the powder obtained in the polymerization in a gaseous phase is carried out in an analogous manner by ~uspending th- powder ~ in a hydrocarbon alcohol mixture.
; Controlllng of the polymeri~ation reaction requires be-2S oldes the usual regulating and mea~uring device~ for tempera-ture, monomer ga~ and molecular weight only withdrawing poly-mer Bamples an~ r~pldly determining the melt lndexes and ~SV
v~luea optionally a~ter a pre~lous treatment wlth ~cetone, 29 Thl~ la a routlne meaaurlng which c~n bo ea~lly e~fected.

~ .

~ C~ 105'~933 It i~ a great advantage of the process according to the in~ention that in the suspension proces~ the quantity of so-: luble polymer contained in the dispersing agent as a result Or the propylene homopolymerization only slightly increases in the course of the copolymerization. ..
:~ The polypropylene molding composition according to tho invention is characterized by a high hardness and toughne~s ~- (=impact strength) Or the molded articles prepared therefrom .~ at low temperatures. It may be u~ed wherever a high meachani- :
~ cal strength (in case of impact or shock) must be assured, `.'. for example in the proces~ing by injection molding for con- .-tainers for the transport and storage of deep frozen food-~ sturf6; for parts in the motor car industry (door handles, .~ rittings, coverings, cases for batteries); in the processing -~ 15 by extrusion for sheets for packaging foodstuff~; for corru- ~ :
.,~ . . :.
gated cardboard for preparing boxes for milk bottles and deep ~
frozen foodstuffs; in the proces~ing by blowing moulding ; ~`
the extruded material for bottles and containers for the transport and storage (small and large ~olume containers). .-Under hardness there is to be understood the ball inten- ..
dation hardness determined according to DIN 53,456 in ~p/cm2. -~; Th- toughness.is the impact streng.th determined according to 8riti~h Standard 2782, part III, method 306 c. The results "~ indicate the falling height of a weight of 1 kg, at which 50 of the tested material still remain undamaged . These indi-~ - cations are in better conformity with practical conditions `
-e than the indicationR of the impact ~trength in mkg.
~ Deep temperatures mean temperatures down to -60C, where-~ 29 by the toughness propert~es are determined in comparison to .. :.: . . ; . ' . : ' . :

HOE 74/~ 101 ~ 105'~933 ~alues at ~23 C, 0C, -30C and -60C.
The RS~ values are determined on solutions of 0.1~ by weight of polymer in decahydronaphtalene at 135 C and indi-cated in deciliter per gram (dl/g).
The me~t indexes MFI 230/5 are determined according to ASTM /D 1238-62/T.
The following examples illustrate the invention.
E X A M P L E 1s .
110 liters of a hydrogsnated aliphatic hydrocarbon having a boiling point range of from 140 to 170 C were introduced into an enamelled 150 l vessel provided with an impoller stirrer, heated to 55 C and saturated with the monomer at a propylene pressure of 0.5 kgjcm .
Poly~erization immediately started after 1 mole of alu-minium diethylmonochloride (= g m-moles/l) and 0.44 n~oles of TlCl3 of the TiCl3 containing component K2 (- 4 m-moles/l) had been added. 32.4 kg of propylene (5.4 kg/h~ were intro- ~ -; duced in the course of 6 hours, whereto hydrogen was added during the first 5 hours for regulating the molecular weight o~ the polypropylene formed. The average hydro~en concen-`` tration in the ga~ zone was 2.j~ by volume ~cf. table). ~en stopping the rnonomer admission the decreasing of the propylene partial pressure was determined by measuring, whereas the total pressure in the vessel was maintained at 1.3 kg/cm by means of nitrogen. A sample of the polymer suspension was wlthdrawn via a dip pipe shortly before the desired par-tial pressure was attained. The mother liquor was filtered off with suction immediate~y and it~ content of soluble poly-29 mer portions was determined by evaporating. The solid poly-~ 13 ~

. . ;
, ,.............................. . . ................ .

Ci 105A~933 mer was washed on a filter with acetone, mixed with a stabili-zing solution (15 ml of CH2Cl2, 0.050 g of 4-hydro~y-3,5-di-ter$iary butyl-phenylpropionic acid stearyl ester and 0.025 g thiopropionlc acid lauryl ester per 10 g of polymer) in 5 a plate glass pan and rapidly dried. Thereafter the melt in-dex 230/5 and the RSV were determined~ which were 12 g/ 1 minutes and 3.03 dl/g respectively. At a propylene residual partial pressure of 0.45 kg/cm2 (~ o.6 kg of dissolved propy-lene~ 2.5 kg of ethylene were homogenuously introduced into the reaction mixture for 60 minutes. A pressure increase could not be noticed during this period. The propylene con-tent of a gas analysis effected thereafter was less than 0.1~ -by ~olume.
In a third reaction step 4.6 kg of ethylene were intro-duced for 60 minutes , corresponding to 11.5~ by weight of the total monomer quantity. Hydrogen was admixed to the mono-mer until its concentration in the gas zone was 3.5~ by vo-lume.
After ha~ing ~dded the monomer it was waited until the pressure in the vessel decreased below 1.2 kg/cm , whereafter the reaction was interrupted by adding 6 liters of iso-propa-nol while destructing the catalyst. -In order to remove residues of the catalyst the reaction product was stirred for 2 and a half hours at 70C and the organic phase was extracted four times with 35 liter of desal-ted water. Thereafter the polymer suspension was filtered and the polymer dried. The yield was 3~ kg, the melt index M~I 230/5=4.4 g/10 minutes, the RSV = 4.36 dl/g and the 29 content of the mother liquor of soluble polymer 2.6~ by weight - 14 _ :

~05'~933 calculated on the total quantity of the polymer.
Table 1 shows the hardness and the impact strength.
E X A M P L E S 2 and 3-Example 1 was repeated twice. The hydrogen partlal pressure was increased each time in the first step of the poly-merization so that a polypropylene having a lower molecular weight was obtained. The average molecular weight of the polymer mixture at the end of the second step, consequently, ;-was lower, too. Further modification can be seen from Table 1.
E X A M P L E S 4 to 6:
The polymerizations were carried out in an analogous -~ manner to example 1, with the modifications indicated in -Table 1 in columns, 3, 4, 5, 9, 13, 14 and 15. The TiC13 containing catalyst component used was the reaction product described above as Kl.-E X A M P L E 7:
Polymerization in the gaseous phase. ~ -In a horizontal 2Q liter reactor provided with scraping `20 stirrer blades 0.1 mole of TiC13 in the form of the component Kl as well as 0.25 mole of aluminium diethyl monochloride in a smaller quantity of pentane were added to 0.3 kg of an im-pact resistant polypropylene material previously prepared.
The mixture was heated to 60C while stirring and propylene was introduced for 4 hours (1.1 kg/h) with 0.2% by volume of `
H2. The pressure increased to 17 kg/cm at the end of the . polymerization and was reduced to 4.5 kg/cm2 by polymerization.
The propylene partial pressure was adjusted to 0.45 kg/cm by expanding the residual quantity of propylene and adding HOE 74~F 101 105'~933 nitrogen. A polymer sample was withdrawn by a lock and ethyl-ene was thereafter introduced firstly alone for 5 minute~ ;~
(t.4 kg/h) and after 30 minutes together with a ~ontent of

3~ by volume of H2 for 45 minutes. The hydro~e~ contont was calculated such that the final melt index ~iFT 2~0~5 was re-duced from 23 g/10 minutes in the polypropylene portion to 3.2 g/10 minutes. After terminating the pol~erization the polymer mixture was withdrawn under nitrogen, and treated while st~rring with 30 liter of an azeotropic mixture of 23~

br weight of n-hexane and 77~ by WQight of iso-propanol for ~,, one hour at 65C in a 70 liter vessel. The polymer powder was then separated from the dispersing agent on a pressure filter and dried under nitrogen. It~ mechanical properties ~
are indicated in Table 1. , , Com~arative example 1 (Comp. ex. 1)s , 110 liters of a hydrogenated aliphatic hydrocarbon having `,' '~
a boiling point range Or rrom 140 to 170 ~ were introduced ,-int,o the apparatu~ ~ccording to example 1, heated to 55C
and saturated with the monomer at a propylene pressure of 0.5 kg/cm2. After having added 1 mole Or aluminium diethyl-monochloride (= 9 m-moles/l~ and 0.44 moles of TiCl3 of the TiC13 containing component K2 (= 4 moles/l) the polymeri-.: .
zation immediately started. 27.8 kg of propylene (3 kg/h) , were introduced in the course Or 9 hours, whereto hydrogen ", ', was added during the first 5 hours for controlling the mole-cular weight of the polypropylene formed . Tho n~erage hy-drogen concentration in the was~ gas (30 liter~/h) was 3.2~
' by volume (see table). Af~er stoppin~ the monomer admi5sion '~' ~ the falling o~ the propylesle partial pre~s~re was determined _ 16 ~
., - ~.
, . ~ - - , ., ` ~

, H~E 74tF 101 (~ 105Z~33 by measurings. Shortly before attaining a propy'ene partial pressure of 2.1 kg/cm a sample of the polymer su~pension was withdrawn and tested as described in exampl~ 1. The melt index was 29 g/10 minutes and the RSV 2.57 dl/g.
Thereafter 3.1 kg of ethylene were introduced homosenu-ously into th~ reaction mix~ure for 75 minutes. A pressure increase could not be noticed during this period; the propy-lene content of a gas analysis effected subsequently was in-~erior to the identification limit of 0.1% by voJu~e~
In the third r0action step 0.4 kg of ethylene were intro-duced for ten minutes corresponding to 1.3~ by weight of the total monomer quantity. No hydrogen was admixed to the monomer.
After having added ethylene the reaction~mixture was treated as described in example 1. The properties of the polymer mixture obtained are indicated in the table.

Comparative oxamples 2 and 3:
20 - The reaction mixture was treated in an analogous manner to example 1 (modifications see table~, but the copolymeri-zation was interrupted as soon as the propylene content in the reaction mixture was below 0.1% by volume so that the polymer mixture did not have a polyethylene portion.
Comparative example 4:
The polymerization was started as in example 1, but ethylene was only introduced when the partial pressure of the propylene wa~ below 0.001 kg/cm2. A very small copolymer 29 portlon was only formed so that the polymer mixture practically ` ' ~.

r~
105,'~933 only consisted of polypropylene and polyethylene.
Com~arative example 5:
A polymer mixture was prepared under the condition~
acoording to example 1, whereby the molecular weight of the 5 propylene portion was reduced owing to the high hydrogen con- ~ , tent in the first step and practically no hydrogen was pre_ sent in the third step so that the molecular weight Or the polyethylene portion was very high.
Com~arative example 6:
The polymerization was anew carried out in an analogous ` ~
manner to example 1, while maintaining a high hydrogen con- -~ -tent in the monomer gas in the third step so that a poly- ,~
ethylene portion of a low molecular weight was obtained.
Comparative examPle 7t : ~:
The example was carried out in an analogous manner to comparative example 6, but by using the TiCl3 component Kl.
~". - - .

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.;
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` ~ ' : ' , HOE 74~F 101 105'~933 T A B L E
Monomer addition and properties of the poLymers *)vessel expand~d from 5 to 0.45 kg/cm first step propylene (C3)-polymerization . . ............................ ...... . ..... __ Ex~mple C total H2 in end of final polypropylene 3 quan- the the pres~ure MFI RSV
tity gas intro- .
of C3 zone dOfcti3on .

; . % by at 2 .
kg/h kg lum~ kg/cm kg/cm2 g/1Omin dl/g .. ' .. _ .
t 1 5.5 33 2.5 2.75 0.45 ~ 12 3.03 .
.' 2 5-5 33 3.2 2.4 0.42 28 2.48 . 3 5-5 33 6.1 2.5 0.28 79 1.88 ~ :
. . . . .
. . 5.5 33 3-5 2.5 -34 38 2.41 .'. 5 5.5 33 3-5 2.5 0.30 40 2.30 5-5 33 4.2 2.7 0-37 73 1.90 7 1.1 4.4 _ 17 (5) 23 2.52 .~ 0.45*) . Comp.
', Ex 1 3.o 27 3.2 2.4 2.1 29 2.57 Ex. 2 3-o 27 2.6 2.6 2.2 14 2.81 Comp .
`~ Ex- 3 3.o 27 3.2 2.4 2.1 29 2.52 ~ Ex. 4 S-'5 33 3-9 2.9 0.001 . 52 2.24 :~ Ex. 5 5-5 33 8.3 3.6 0.37 118 1.77 Comp.
' Ex. 6 5-5 33 4.1 2.1 0.34 6.6 3.28 Ex. 7 5-5 33 1.8 2.1 0.30 4.8 3-39 _ 19 _ .~ .

, .. . . .

- , HoE14/F` 101 O 105~933 ~ -T A ~ L E

~ second 9 tep ,,.~ , C3/C2 - copolymeriz8tion ' .~-... , .. ,, , ,., . . -:. Example C2 C2 copolymeri~ate ,.~
total C~ RSV~ by weight ;.
portion of total m . ~ by polymer ., kg/h kg w~ight dl/g ~
.. , . 8 9 10 11 12 ,....................... ... ,_ .......................... .. ,_ , 1 2.5 2.5 16 3.6 7-7 ~ ~ -:~ 2 2.5 2.1 22 3.1 6.3 ~ ~.
.~ . 3 2.5 1.9 17 2.1 5-5 ~ ~.
.~ 4 2.5 2.1 19 2.9 6.1 2.5 2.0 17 2.9 5-7 ;~ 6 2-5 1.8 18 2.4 5.2 ~ 7 1.4 0.1 17 2.1 2.2 .'`.',' ., ' . . .. ~:
.
.-Comp. Ex. 1 2.5 3.1 30 1.3 14 Comp. Ex. 2 2.5 1.7 45 1.7 11 , . Comp. Ex. 3 2.5 2.4 35 1.Z 13 `~j Comp. ~x. 4 2.5 0.2 _ _ -7 , Comp. Ex. 5 2.5 2.5 17 1.6 7.1 : -~,' Comp. Ex. 6 2.5 3.0 . 14 2.1 7-9 :~
Comp. Ex. 7 2-5 2.4 14 2.7 6.4 ~.~ . , .' . ~ i~
~' , ~
~ 20 ~

` ; . , , }IOF, 74/F 101 ~3 105;~933 T A B L E
*)heptane extract third step ethylene t= C2) ~ polymerization ~, . _ ExampleC2 C2 ~2 PE ~oluble poly-total gas ~ by mer in mother - zone weight of to-, tlymePr~

kg/h kg volume ~ % by weight _ . . ~-~; 1 4.6 4.6 11 11.5 2.6 2 2.5 7.1 28 17 ~ 3.2 3 2.5 6.7 23 16 2.9

4 2.5 7.1 31 17 4.1 2.5 7.1 20 17 4.4 6 2.5 7.1 27 17 3.6 7 1.4 1.0 _ 20 4.2*) .. ~ , .
,.

Comp. Ex. 1 2.5 0.4 _ 1.3 3.8 Comp. Ex. 2 _ _ _ _ 3-2 ~, Comp. Ex. 3 _ _ _ _ 1.5 Comp. Ex. 4~ 2.5 10.3 3.9 24 2.4 ~i Comp. Ex. 5 2.5 7.o ~ 0.1 16.5 3-9 Comp. E;;. 6 2.5 8.3 44 19 4.1 ' Comp. Ex. 7 2.5 6.7 33 15 3-7 . . . ,' - 21 _ ~ ' .

. .

, HOE 74/F ? 1 C~ lOS'~933 ~ ~-:~ T A B L E 1 :
. ~, ,.

'' . .:
., Properties of the moulding compo~ition _ -- ~
` Example MFI RSV ball in-fall test ~. .:~; dentation i~ hardnes 5 ~ +23C 0C -30C -60C
,'.,................................................................... .. ,-. g/10 min dl/g kg/cm2 cm cm cm cm ' ~ _ . _ .. " ' -~i, 1 4.4 4.36 630 180150 115 70 2 11 3.80 650 190155 120 50 3 22 3.19 685 145115 85 45 ~, 9-3 4.13 675 185 155 - 130 60 12 4.05 675 170 150 135 70 7 - 3.2 4.14 640 190 170 110 45 . . . ,'~
' . . ,,- ~, Comp. Ex. 1 2.0 3-98 - 500 170 160 120 ' ~ Comp. Ex. 2 12 2-95 580 140 120 60 Comp. Ex. 3 17 2.78 610 135 115 60 _ ~ -~
3 Comp. Ex. 4 19 3-10 720 110 85 15 Comp . Ex . 5 1.6 3.68 630 160 130 1 0 5 1 S
- Comp. Ex. 6 25 4~ 600 lS 135 110 20 '! . 'Comp~ Ex- 7 4-9 5~ 19 630 165 115 80 25 ~, ~. . . .

~ ~ 22 _ ., : : : . .. ., ,, . . - .

.: . . .

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A polypropylene moulding composition comprising from 70 to 90% by weight of polypropylene, 2 to 10% by weight of an ethylene/propylene copolymer, the molar ratio of ethylene to propylene being in the range of from 90:10 to 25:75 and 8 to 25% by weight of a polyethylene, wherein the melt index MFI 230/5 of the moulding composition is inferior to that of the polypropylene contained therein and superior by the coefficient 1.3 to 7.0 to that of a polypropylene prepared by means of the same catalyst as the moulding com-position and having the same reduced specific viscosity.

2. A polypropylene moulding composition as claimed in claim 1 in which the reduced specific viscosity of the ethylene/
propylene copolymer is at least 2.0 dl/g.

3. A polypropylene moulding composition as claimed in claim 1 comprising from 75 to 85% by weight of polypropylene, 3 to 8% by weight of ethylene/propylene copolymer and 12 to 17% by weight of polyethylene.

4. A polypropylene moulding composition as claimed in claim 1, claim 2 or claim 3 in which the melt index of the moulding composition is superior by the coefficient of 2.0 to 5.0 to that of a polypropylene prepared by means of the same catalyst as the moulding composition and having the same reduced specific viscosity.

5. A process for the preparation of a polypropylene moulding composition as claimed in claim 1 in which (a) a polypropylene having a melt index 230/5 of from 5 to 80 g/10 minutes is prepared by polymerizing propylene at a pressure of from 0.5 to 40 kg/cm2 and a temperature of from 40 to 110°C, in the presence of a TiCl3-containing catalyst and of from 0.1 to 20% by volume of hydrogen, calculated on the quantity of the propylene, (b) ethylene is introduced in a second step at a propylene partial pressure of less than 0.5 kg/cm2 and an ethylene/
propylene copolymer is formed at a pressure of from 0.5 to 40 kg/cm2 and a temperature of from 40 to 110°C and (c) a polyethylene is prepared in a third step at a propylene partial pressure of less than 0.001 kg/cm2 and a total pressure of from 0.5 to 40 kg/cm2, a temperature of from 40 to 110°C in the presence of from 1 to 50% by volume of hydrogen.

6. A process as claimed in claim 5 in which the TiCl3-containing catalyst is formed by reducing TiCl4 with a member of the group of aluminium, aluminium diethylchloride and al-uminium ethylsesquichloride and submitting the product to a thermal treatment using aluminium diethylmonochloride as activator.

7. A process as claimed in claim 5 or claim 6 in which the polymerization is carried out continuously and in which two reactors are used for the second processing step and the propylene concentration in the second reactor is maintained at a lower level than that in the first reactor.

8. A process as claimed in claim 5 or claim 6 in which the polymerization in the second step is effected in a reaction tube in which the reflux is insignificant and the ethylene is added so that its concentration in the reaction mixture is lower at the beginning of the tube than at the end.